An experimental coronavirus vaccine developed by Johnson & Johnson protected monkeys from infection in a new study. It is the second vaccine candidate to show promising results in monkeys this week.
The company recently began a clinical trial in Europe and the United States to test its vaccine in people. It is one of more than 30 human trials for coronavirus vaccines underway across the world. But until these trials are complete — which will probably take several months — the monkey data offers the best clues to whether the vaccines will work.
“This week has been good — now we have two vaccines that work in monkeys,” said Angela Rasmussen, a virologist at Columbia University who was not involved in the studies. “It’s nice to be upbeat for a change.”
But she cautioned that the new results shouldn’t be used to rush large-scale trials in humans. “We just can’t take shortcuts,” she said.
Unlike many other vaccines in development that might require two injections, the Johnson & Johnson candidate shielded the monkeys with just one dose, according to a study published on Thursday in Nature.
“It’s a very reassuring level of protection we saw,” said Dr. Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston and a co-author of the new study.
The study comes just two days after a similar one was published on a vaccine tested by Moderna and the National Institutes of Health.
But the two vaccines work in very different ways.
The Moderna vaccine delivers a kind of genetic material called “messenger RNA” into cells.
The cells use the vaccine RNA to produce a protein found on the surface of the coronavirus, called spike protein, which then hopefully prompts an immune response.
RNA-based vaccines are being tested for a number of diseases, but none have yet been licensed for use in people.
In the Moderna study, researchers vaccinated monkeys by giving them two shots spaced over four weeks. A month later, they infected the animals with the coronavirus. In some of the vaccinated monkeys, researchers could not detect the virus in the nose or lungs. In others, the virus replicated slowly before disappearing.
Moderna began Phase 3 trials of its mRNA vaccine on Monday, as did Pfizer, which is testing its own mRNA vaccine.
The Johnson & Johnson vaccine, in contrast, is based on a virus called Ad26, which researchers have modified so that it carries the coronavirus spike protein gene. The Ad26 virus can slip into human cells, but cannot replicate once inside them. Its host cell then uses the spike gene to make the coronavirus proteins.
This month, European regulators approved Johnson & Johnson’s Ad26 vaccine for Ebola. It was the first time this kind of virus-assisted gene delivery was approved for any disease.
In March, Dr. Barouch and his colleagues designed seven variants of an Ad26 vaccine for the coronavirus. They made tiny changes to the spike gene to see whether they could get cells to make more copies of the viral protein. They also tested variants that would make the spike protein more stable, which might prompt a stronger immune response.
Based on earlier research, Dr. Barouch and his colleagues suspected that the Ad26 vaccine would be very potent. They decided to run their experiment using just one dose, to see whether that was enough to provide immunity.
After a single injection of the vaccine, they waited six weeks and then infected the animals with the coronavirus. Six of the seven vaccine variants offered monkeys partial protection against the coronavirus, meaning that the virus replicated only at low levels in the animals.
The seventh version proved more powerful than the rest: Five out of six monkeys that received it had no detectable viruses at all. The sixth had only low levels in its nose.
“The fact that we could protect with a single shot in animal models was quite a positive surprise to us,” said Dr. Paul Stoffels, the chief scientific officer of Johnson & Johnson.
It was this best-performing vaccine that Johnson & Johnson used last week to begin its first human safety trial, a so-called Phase 1 trial. If it goes well, the company hopes by September to enter Phase 3 trials, which test not only whether the vaccine is safe, but also whether it works.
The company plans on testing both single and double doses. Dr. Rasmussen said that a vaccine that proved effective with a single dose would make it far easier to treat the billions of people who need it. “Theoretically, you would need less of it, so you give it to more people more quickly,” she said.
Inovio, a company developing a DNA-based vaccine, announced Thursday that monkeys challenged four months after vaccination had a reduced load of the virus in their nose and lungs. Their report has not yet been published in a scientific journal.
AstraZeneca and the University of Oxford have developed a vaccine based on yet another type of modified virus, called ChAdOx1. In May, they released promising monkey data, which was also published on Thursday in Nature. The team is now running Phase 3 trials in people, which could produce results by October.
“It’s exciting to see the number of platforms that are showing promise for a vaccine,” said Stacey L. Schultz-Cherry, a virologist at St. Jude Children’s Research Hospital in Memphis who was not involved in any of the trials.